Mybatis SQL映射语句中参数注释规则

最近在*Mybatis*的学习中对于映射语句中的参数注释设置有点犯迷糊，于是在*debug*下跟踪了下源代码，发现*Mybatis*在接口方法映射语句中会做如下处理：

1. 接口方法只有一个参数

1.1 不使用`@Param`注解

1.1.1 参数为基本类型或为基本包装类型(int,Integer,String...)

参数注释为: #{任意字符}

1.1.2 参数为自定义对象

参数注释为: #{对象属性}

示例：

[java] view plaincopy

<span mce_style="font-size: medium;" style="font-size:14px; "> User getUserById(int id);

// 注：该中情况下'任意字符'不能为空，否则报错

// select * from <TABEL> where id = #{任意字符}

select * from <TABLE> where id = #{id}

User getUser(User user); // user.getName user.getAge

select * from <TABLE> where name = #{name} and age = #{age}</span>

1.2 使用`@Param`注解

1.2.1 参数为基本类型或为基本包装类型(int,Integer,String...)

参数注释为: #{注解名称} | #{param1}

1.2.2 参数为自定义对象

参数注释为: #{注解名称.对象属性} | #{param1.对象属性}

示例：

[java] view plaincopy

<span mce_style="font-size: medium;" style="font-size:14px; "> User getUserById(@Param(value="keyId") int id);

select * from <TABEL> where id = #{keyId}

// or

select * from <TABLE> where id = #{param1}

User getUser(@Param(value="usr") User user); // user.getName user.getAge

select * from <TABLE> where name = #{user.name} and age = #{user.age}

// or

select * from <TABLE> where name = #{param1.name} and age = #{param1.age}</span>

2. 接口方法有两个及两个以上参数

2.1 不使用`@Param`注解

2.1.1 参数为基本类型或为基本包装类型(int,Integer,String...)

参数注释为: #{参数位置[0..n-1]} | #{param[1..n]}

2.1.2 参数为自定义对象

参数注释为: #{参数位置[0..n-1].对象属性} | #{param[1..n].对象属性}

示例：

[java] view plaincopy

<span mce_style="font-size: medium;" style="font-size:14px; "> User getUser(String name, int age);

select * from <TABLE> where name = #{0} and age = #{1}

// or

select * from <TABLE> where name = #{param1} and age = #{param2}

User getUser(User usr, int flag);

select * from <TABLE> where name = #{0.name} and age = {0.age} and flag = #{1}

// or

select * from <TABLE> where name = #{param1.name} and age = {param1.age} and flag = #{param2}</span>

2.2 使用`@Param`注解

2.2.1 参数为基本类型或为基本包装类型(int,Integer,String...)

参数注释为: #{注解名称} | #{param[1..n]}

2.2.2 参数为自定义对象

参数注释为: #{注解名称.对象属性} | #{param[1..n].对象属性}

示例：

[java] view plaincopy

<span mce_style="font-size: medium;" style="font-size:14px; "> User getUser(@Param(value="xm") String name, @Param(value="nl") int age);

select * from <TABLE> where name = #{xm} and age = #{nl}

// or

select * from <TABLE> where name = #{param1} and age = #{param2}

// or

select * from <TABLE> where name = #{xm} and age = #{param2}

User getUser(@Param(value="usr") User user, @Param(value="tag") int flag);

select * from <TABLE> where name = #{usr.name} and age = #{usr.age} and flag = #{tag}

// or

select * from <TABLE> where name = #{param1.name} and age = #{param1.age} and flag = #{param2}

// or

select * from <TABLE> where name = #{usr.name} and age = #{param1.age} and flag = #{param2}</span>

2.2.3 部分参数使用`@Param`注解

当采用部分参数使用`@Param`注解时，参数注释为将以上两种情况结合起来即可。

示例：

[java] view plaincopy

<span mce_style="font-size: medium;" style="font-size:14px; ">User getUser(String name, @Param(value="nl") age, int gendar);

// 对于age的访问不能是 #{1} 只能是 #{param2} | #{nl}

select * from <TABLE> where name = #{0} and age = #{nl} and gendar = #{param3)</span>

总结下

`@Param`的作用是设置参数别名。设置后的参数只能通过`#{param[1..n]`或者`#{注解别名}`来访问

多个参数情况下，均可使用 `#{参数位置[0..n-1]}` | `#{param[1..n]}`来访问参数

最后给出几个源代码中关于参数设置的源代码供大家参考：

参数获取操作：org.apache.ibatis.binding.MapperMethod.getParam(Object[] args)

[java] view plaincopy

<span mce_style="font-size: medium;" style="font-size:14px; "> private Object getParam(Object[] args) {

final int paramCount = paramPositions.size();

// 无参数

if (args == null || paramCount == 0) {

return null;

// 无注解并参数个数为1

} else if (!hasNamedParameters && paramCount == 1) {

return args[paramPositions.get(0)];

} else {

Map<String, Object> param = new MapperParamMap<Object>();

for (int i = 0; i < paramCount; i++) {

param.put(paramNames.get(i), args[paramPositions.get(i)]);

}

// issue #71, add param names as param1, param2...but ensure backward compatibility

// 这就是 #{param[1..n]} 的来源

for (int i = 0; i < paramCount; i++) {

String genericParamName = "param" + String.valueOf(i + 1);

if (!param.containsKey(genericParamName)) {

param.put(genericParamName, args[paramPositions.get(i)]);

}

}

return param;

}

}</span>

SQL预编译参数设
置：org.apache.ibatis.executor.parameter.DefaultParameterHandler.setParameters(PreparedStatement
ps) throws SQLException

[java] view plaincopy

<span mce_style="font-size: medium;" style="font-size:14px; ">org.apache.ibatis.executor.parameter.DefaultParameterHandler.setParameters(PreparedStatement ps) throws SQLException

public void setParameters(PreparedStatement ps)

throws SQLException {

ErrorContext.instance().activity("setting parameters").object(mappedStatement.getParameterMap().getId());

List<ParameterMapping> parameterMappings = boundSql.getParameterMappings();

if (parameterMappings != null) {

MetaObject metaObject = parameterObject == null ? null : configuration.newMetaObject(parameterObject);

for (int i = 0; i < parameterMappings.size(); i++) {

ParameterMapping parameterMapping = parameterMappings.get(i);

if (parameterMapping.getMode() != ParameterMode.OUT) {

Object value;

String propertyName = parameterMapping.getProperty();

PropertyTokenizer prop = new PropertyTokenizer(propertyName);

if (parameterObject == null) {

value = null;

} else if (typeHandlerRegistry.hasTypeHandler(parameterObject.getClass())) {

value = parameterObject;

} else if (boundSql.hasAdditionalParameter(propertyName)) {

value = boundSql.getAdditionalParameter(propertyName);

} else if (propertyName.startsWith(ForEachSqlNode.ITEM_PREFIX)

&& boundSql.hasAdditionalParameter(prop.getName())) {

value = boundSql.getAdditionalParameter(prop.getName());

if (value != null) {

value = configuration.newMetaObject(value).getValue(propertyName.substring(prop.getName().length()));

}

} else {

value = metaObject == null ? null : metaObject.getValue(propertyName);

}

TypeHandler typeHandler = parameterMapping.getTypeHandler();

if (typeHandler == null) {

throw new ExecutorException("There was no TypeHandler found for parameter " + propertyName + " of statement " + mappedStatement.getId());

}

JdbcType jdbcType = parameterMapping.getJdbcType();

if (value == null && jdbcType == null) jdbcType = configuration.getJdbcTypeForNull();

typeHandler.setParameter(ps, i + 1, value, jdbcType);

}

}

}

}</span>